Document 4089

Radon and Lung Cancer Risk: Taking Stock at the Millenium
Jonathan M. Samet1 and George R. Eradze2
'Department of Epidemiology, Johns Hopkins University School of Hygiene and Public Health, Baltimore, Maryland, USA; 2Department of
Preventive Medicine, Tbilisi State Medical University, Tibilisi, Georgia
brought into the mine dissolved in water. In
homes, the principal source is soil gas, which
penetrates through cracks or sumps in basements or around a concrete slab. Because uranium-238 is universally present in the earth,
radon is a ubiquitous indoor air pollutant,
and it is also present in outdoor air, albeit at
far lower concentrations. Infrequently, building materials or water also may contribute
significantly to indoor concentrations.
Radon is an alpha emitter that decays
with a half-life of about 3.5 days to a shortlived series of progeny (Figure 1) (1). Unlike
radon, the progeny are solid and form into
small molecular clusters or attach to aerosols
Radon, discovered early in the 20th century uncertainties, and further gains in knowledge in the air after their formation. The inhaled
as an emanation from radium, is now a well- can be projected. Mechanistic research on the particulate progeny may be deposited in the
characterized human carcinogen. An exten- consequences of cellular irradiation by alpha lung on the respiratory epithelium; radon by
sive scientific literature based in experimental partides, directly responsible for the causation contrast is largely exhaled, although some
and observational data addresses mechanisms of cancer by radon, will enhance certainty and radon is absorbed through the lung. Radon
of action at the cellular and molecular levels, eventually support the development of biologi- itself is not responsible for the critical dose of
exposures and doses in occupational and gen- cally based models. In the wealth of data radioactivity delivered to the lung that causes
eral environmental settings, and cancer risk, already available and with these exciting cancer. While radon was initially thought to
along with modifiers of risk such as smoking. prospects for evolution of the evidence, radon be the direct cause of the lung cancer in the
This literature has been frequently reviewed carcinogenesis offers a superb model for link- miners, Bale (6) and Harley (7) recognized in
the early 1950s that alpha particle emissions
and summarized, most recently in the report ing from research to risk assessment to policy.
from radon progeny and not from radon itself
of the National Research Council's Biological
Effects of Ionizing Radiation (BEIR) VI Radon and Lung Cancer: An Overview were responsible for the critical dose of radiaCommittee (1) released in 1998. The final The story of radon as a cause of lung cancer is tion delivered to the lung. Alpha decays of
report was published in 1999. That report a long one with historical accounts document- two radioisotopes in the decay chain,
comprehensively reviewed the literature and ing a fatal lung disease centuries ago in miners polonium-218 and polonium-214 (Figure 1),
offered new models for estimating the lung working in the Erz Mountains of Eastern deliver the energy to target cells in the respiracancer risk associated with radon exposure. Europe (5). Over a century ago, the miners tory epithelium that is considered to cause
The present review does not replicate that were found to have thoracic malignancy, later radon-associated lung cancer (8). Alpha particoverage, and readers seeking a summary of identified as primary lung cancer. By early in cles, equivalent to a helium nucleus, are
the scientific evidence should turn to the the 20th century, levels of radon in the mines charged and have a high mass. Although their
in this region were measured and found to be range of penetration into tissues is limited,
BEIR VI report or other recent reviews (2,3).
After a brief synthesis of the current state quite high; the hypothesis was soon advanced they are highly effective at damaging the
of knowledge of radon and cancer, this that radon was the cause of the unusually high genetic material of cells. As reviewed in the
review looks to future needs for research on rates of lung cancer. Although not uniformly report of the BEIR VI Committee (1), pasradon, both for public policy purposes and accepted initially, as the findings of epidemio- sage of even a single alpha particle through a
for advancing understanding of radon car- logic studies of underground miners were cell can cause permanent genetic change in
cinogenesis. In fact, our knowledge of the reported from the 1950s on, there soon was the cell.
Evidence on radon and lung cancer risk is
risk posed by radon is relatively advanced substantial evidence showing that radon was a
compared to that on many other human car- cause of occupational lung cancer (1,5). In now available from approximately 20 different
cinogens. However, the public policy impli- fact, the more recent concern about radon in epidemiologic studies of underground miners,
cations of indoor radon are so sweeping that the air of homes was initially driven by the
a high level of certainty has been sought by strong evidence that radon causes lung cancer
This article is part of the monograph on Environmental
policymakers about the risks of the low levels in underground miners.
Radon is a noble and inert gas resulting and Occupational Lung Diseases.
of exposures generally found in homes.
Address correspondence to J.M. Samet,
Questions have been raised about the scien- from the decay of naturally occurring ura- Department
of Epidemiology, Johns Hopkins
tific basis for the U.S. Environmental nium-238. With a half-life of over 3 days, University School of Hygiene and Public Health, 615
USA.
Protection Agency's (U.S. EPA) Radon radon has time to diffuse through rock and N. Wolfe St., Suite 6041, Baltimore, MD 21205
(410) 955-3286. Fax: (410) 955-0863.
Program since its inception in the early soil after it forms and before undergoing fur- Telephone:
E-mail: [email protected]
1980s (4). Mounting epidemiologic and lab- ther decay into its particulate progeny. In
Received 23 September 1999; accepted 25
oratory research have steadily reduced critical mines, it enters the air from the ore or is February 2000.
Radon is a well-established human carcinogen for which extensive data are available, extending into
the range of exposures experienced by the general population. Mounting epidemiologic evidence on
radon and lung cancer risk, now available from more than 20 different studies of underground miners
and complementary laboratory findings, indicates that risks are linear in exposure without threshold.
Radon is also a ubiquitous indoor air pollutant in homes, and risk projections imply that radon is the
second leading cause of lung cancer after smoking. Recommended control strategies in the United
States and other countries, which include testing of most homes and mitigation of those exceeding
guideline levels, have been controversial. Further research is needed, drawing on molecular and
cellular approaches and continuing the follow-up of the underground miner cohorts, and scientists
should work toward constructing mechanistically based models that combine epidemiologic and
experimental data to yield risk estimates with enhanced certainty. Key words: lung cancer, radon,
radon progeny, risk assessment. - Environ Health Perspect 1 08(suppl 4):635-641 (2000).
http.//ehpnetl.niehs.nih.gov/docs/2000/suppl-4/635-64 lsamet/abstracthtml
Environmental Health Perspectives * Vol 108, Supplement 4
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SAMET AND ERADZE
including 11 studies that provide quantitative
information on the exposure-response relationship between exposure to radon progeny
and lung cancer risk (1,5). Occupational risks
of radon-caused lung cancer have been
described in many reports on the findings of
the individual studies and in several pooled
analyses of the data from the 11 studies with
quantitative information (1,10). There is a
surprising degree of consistency among the
risks estimated in these studies; the risk coefficients span approximately a single order of
magnitude, in spite of substantial methodologic differences among the studies (1). In
general, the temporal patterns of excess risk
following exposure are also similar among the
studies; that is, risks change in a similar fashion with time since exposure and with age of
the individual.
Although radon progeny are now a wellrecognized occupational carcinogen, radon
became a topic of controversy again in the
1970s and 1980s because it was found to be a
ubiquitous indoor air pollutant in homes,
and recommended control strategies in the
United States and other countries included
testing of most homes and mitigation of
those levels exceeding suggested guidelines
(4). Radon was found to be present in indoor
air as early as the 1950s, but potential health
implications received little notice until several
decades later. The problem first received the
greatest attention in Scandinavia, but homes
with radon levels of concern have now been
identified in other countries of Europe and in
North America. Housing surveys show that
radon is ubiquitous and that concentrations
tend to follow a log-normal distribution
(Figure 2). Policies are now in place in many
countries to manage the lung cancer risk associated with indoor radon. These policies
involve identification and mitigation of radon
levels in homes with concentrations above
guideline values and use of construction techniques that reduce radon concentrations.
Since these policies potentially extend to
almost all residential housing, their scientific
base has been challenged, as has their cost
effectiveness.
Initially, risks of indoor radon were estimated primarily by extrapolating the risks
observed in the studies of underground miners to the exposures sustained by the general
population indoors. In this risk assessment
approach, key uncertainties reflected the use
of risk estimates from relatively short-term
exposures at concentrations substantially
above those typically found in homes, the
extension of estimates from men, largely
smokers, to the entire population, and differing dosimetry of radon progeny for the circumstances of exposures in mines and in
homes. Linear nonthreshold models were
used for the extrapolation from higher to
..l.s s1
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:tal
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Radon
H
r
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'.rideb progeny
lower exposures, which invited the criticism
that risks were overestimated. Lung models
were used to address the potential uncertainty
from differing dosimetries in homes and
mines, with the finding that exposure-dose
relations were quite comparable for the miners and for the general population (8).
To develop risk estimates directly from
the general population, case-control studies
were initiated beginning in the 1980s (1,5).
The basic design of these studies involved
comparison of estimated radon exposures for
lung cancer cases with those of appropriate
controls. Radon exposures were estimated by
making measurements of radon concentrations, generally over several months to a year,
in the current and former residences of cases
and controls. The case-control studies were
soon recognized as being subject to substantial bias toward a null finding because of
unavoidable errors in the exposure estimates;
such errors arose from missing data and
errors in the radon measurements (11).
Consequently, plans were made for pooling
the data from the individual studies (12).
Initial pooling of data from North America
and Europe is now in progress and a pooling
of all of the studies should be completed by
approximately 2002. In the meantime, the
findings of the completed studies have been
combined using meta-analysis (1,13). The
risk estimate derived from the eight completed studies is indicative of an effect fully
consistent with the risk extrapolations from
the miner studies (Figure 3).
Although risk management for indoor
radon remains controversial, the evidence on
radon and lung cancer is now very extensive.
Initially, epidemiologic and other research
was driven by the need to characterize the
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Figure 1. The radon-decay chain. An arrow pointing downward indicates decay by alpha-particle emission; an arrow
pointing to the right indicates decay by beta-particle emission The historical symbols for the nuclides are in parentheses below the modern symbols. Most decay takes place along the unbranched chain marked with thick arrows.
The negligible percentage of decay along the thin arrows is shown at critical points The end of the chain lead 206,
is stable not radioactive. Half-lives of each isotope are shown as seconds (s), minutes (m), days (d), or years (y).
Modified from the National Research Council (1).
636
Figure 2. Distribution of radon concentrations in U.S.
homes. Modified from the U.S. EPA (4).
Environmental Health Perspectives
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RADON AND LUNG CANCER RISK: TAKING STOCK
risks faced by underground miners in order to
set exposure limits that would have acceptable
risks. This work emphasized epidemiologic
approaches, but animal studies were also conducted to confirm the hazard and to address
the modifying effects of such factors as the
presence of ore dust and diesel exhaust, cigarette smoking, and dose rate (14). More
recently, research has reflected the need to
understand better the risks posed to the general population by indoor radon. Epidemiologic studies have been conducted to assess
directly the general population's risk of lung
cancer from indoor radon; laboratory studies
using molecular and cellular approaches have
been conducted to better understand the
mechanism of radon carcinogenesis and to
address key uncertainties in assessment of the
risks of indoor radon.
Over the last several decades, risk models
have been developed for risk assessment and
risk management of indoor radon. However,
lung cancer risk in underground miners has
long been of interest; in fact, the first attempt
to quantify risk was made by Evans and
Goodman (15) in their 1940 report based
on the radon measurements made in the
Schneeburg and Joachimsthal mines. Key
reports have come from the International
Commission for Radiological Protection
(ICRP), the National Council for Radiation
Protection and Measurements, and the BEIR
Committees of the U.S. National Research
Council. Samet (16) has reviewed the evolution of risk assessment for radon and lung
cancer. To illustrate the contemporary
approach to radon risk assessment, the models developed by the BEIR VI Committee are
described below.
Conceptually, the BEIR VI Committee
extended the approach used a decade earlier
30 -
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11
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,
100
300
200
400
Rn concentration (Bq/m3)
----------
Pooled miner estimates
Relative risk= 1
RR for study:
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Finland-Il
v Sweden
V Stockholm
A
Shenyang
A Winnipeg
0 Missouri
0 New Jersey
Figure 3. Relative risks from 8 lung cancer case-control
studies of indoor radon. - - - -, extrapolation of risk from
miners (10). . relative risk of 1.
by the BEIR IV Committee, i.e., developing
an empiric, time-dependent model for lung
cancer risk from the miner data and then
extending that model to the general population with consideration of the possibility of
differing exposure-dose relations in homes
and in mines and of smoking, the most critical potential modifying factor. The BEIR VI
Committee used the pooled data set from the
11 miner cohorts and the 1994 analysis of
Lubin et al. (10) as a starting point for developing its risk models (1). The pooled data set
included more than 2,700 lung cancer deaths
among 68,000 miners followed for nearly 1.2
million person-years of observation. This data
set was substantially larger than that considered by the BEIR IV Committee.
Most analyses were based on a linear
excess relative risk (ERR) model:
than projected from estimates made at the
generally higher exposures experienced by the
miners. The extent of the information available at lower levels of exposure permitted
analyses of risks in a range of exposures of
greatest relevance to exposures associated with
indoor radon. With the data restricted to
cumulative exposures below 200 WLM, there
was no evidence for departure from a linear
model and the exposures were in a range at
which an inverse dose-rate effect was not
expected on a biophysical basis (1).
The BEIR VI (1) report provides risk estimates for various scenarios of exposure to
radon and also makes projections of the burden of lung cancer in the United States
attributable to radon progeny (Table 1).
These estimates are provided in Table 1,
which includes the figures for the total population and for smokers and never-smokers
RR = 1 + iw or ERR = iw,
separately. The estimates for smokers and
never-smokers are based on the assumption of
where RR is relative risk, P is a parameter a submultiplicative combined effect of smokmeasuring the unit increase in ERR per unit ing and radon progeny. The submultiplicaincrease in w, and w is cumulative exposure tive relationship was estimated from the
to radon progeny in WLM (working level studies with data available on both smoking
months is the unit of exposure used for and exposure to radon progeny; it implies
undergound miners; lifetime exposure synergism between the two factors, but the
indoors is approximately 14 WLM). As in the degree of synergism is less than fully multiBEIR IV analysis, ERR was linearly related to plicative. Estimates based on the BEIR IV
cumulative exposure to radon progeny. The model are included in the tables along with
ERRIWLM varied significantly with other estimates based on fitting a constant relative
factors; it decreased with attained age, time risk model to the data at exposures less than
since exposure, and time after cessation of 50 WLM, the lowest level of exposure with
exposure but was not affected significantly by sufficient data available for analysis. The
age at first exposure. Over a wide range of BEIR VI report also includes a quantitative
total cumulative exposures to radon progeny, uncertainty analysis.
lung cancer risk was increased as exposure
These estimates confirm that radon prograte declined, confirming the pattern reported eny should be considered a significant cause
from the Colorado Plateau study (17), and of lung cancer in the United States. The
supporting the prior hypothesis of an inverse attributable risks are higher on a percentage
dose-rate effect (18). The inverse dose-rate basis for never-smokers than smokers, reflecteffect implies that the lower rates of exposure, ing the submultiplicative interaction between
typical of homes, could increase risk more smoking and radon progeny. The numbers of
Table 1. Estimated attributable riska for lung cancer death from domestic exposure to radon using 1985-1989 U.S.
population mortality rates based on selected risk models.
Model
Ever-smokersb
Population
Never-smokersb
Males
Committee's preferred models
0.141
0.125
Exposure-age-concentration
0.258
0.099
0.087
Exposure-age-duration
0.189
Other models
CRRc (< 50 WLM)
0.109
0.096
0.209
BEIR IV
0.082
0.071
0.158
Females
Committee's preferred models
0.137
0.269
0.153
Exposure-age-concentration
0.108
0.096
0.197
Exposure-age-duration
Other models
0.114
0.101
0.209
CRR ( 50 WLM)
BEIR IV
0.077
0.087
0.163
CRR, constant relative risk.
'The risk of lung cancer death attributed to radon in populations exposed to radon divided by the total risk of lung cancer death in a
population. bBased on a submultiplicative relationship between tobacco and radon. Data from the National Research Council I1).
Environmental Health Perspectives * Vol 108, Supplement 4 * August 2000
637
SAMET AND ERADZE
attributable cancer deaths are far higher in
smokers than in never-smokers. Of the lung
cancer deaths attributed to radon exposure,
only a minority can be prevented by current
risk management strategies, as the total number of deaths attributed can, in theory, be
prevented only by lowering levels of radon
progeny indoors to outdoor values. For the
United States, about one-third of the radonrelated lung cancer deaths are attributed to
concentrations above the current guideline of
the U.S. EPA.
Open Quiestions Concerning Radon
and Lung Cancer
As evident from even this brief review, we have
a broad and rich evidence base on radon and
lung cancer, one that has proved sufficient for
developing policies for radon control. Yet, policy makers are seeking greater certainty and
there are still open scientific questions to be
investigated. Additionally, there is the potential for combining laboratory-based understanding of mechanisms with observational
data to develop a true, biologically based risk
model. These questions and potential research
approaches are discussed in the next section.
What Is the Mechanism of Radon
Carcinogenesis?
We are poised to make substantial advances
in our understanding of mechanisms of carcinogenesis by alpha particles, which are
directly responsible for the induction of lung
cancer by radon. The BEIR VI Report (1)
provides an overview of recent advances in
the molecular and cellular basis of cancer causation by alpha particles and directly links
these advances to their risk assessment implications. This synthesis makes clear the linkages between molecular and cellular research
and key uncertainties in risk assessment: the
assumption of a linear nonthreshold model at
the lowest levels of exposure and the magnitude and existence of dose-rate effects at low
levels of exposure. Experimental systems have
also been designed to explore combined
effects of radon exposure and tobacco smoking, but these models cannot replicate the
complex and sustained exposure to carcinogens and irritants typical of human smoking.
New experimental methods involving single-cell irradiation with alpha particles appear
particularly promising as tools for exploring
the effects of alpha particles on the cell (159.
Using this experimental model, it is possible
to characterize effects on cells using single
particles of varying energy and to explore the
consequences of multiple versus single hits to
the cell nucleus. Permanent cellular changes
following single-cell irradiation were considered by the BEIR VI Committee as evidence
of the appropriateness of assuming a linear
nonthreshold relationship between exposure
638
and lung cancer risk. Further advances in our
understanding of the basis of radon carcinogenesis are likely to bring the greatest gain in
certainty for risk models for the future, as we
have already completed a relatively complete
synthesis of the epidemiologic evidence.
What Is the Risk of Typical Indoor
Radon Concentrations?
In the United States and other countries for
which survey data are available, the concentrations of radon in homes follow an approximately log normal distribution (Figure 2).
For risk management purposes, we consequently need estimates of the risks of the high
end of the distribution (which overlaps substantially with the concentrations at which
miners were exposed) and of the risks at typical indoor levels (which are much lower than
those to which the miners were exposed in
the epidemiologic studies). The population's
burden of attributable risk is driven by the
broad end of the distribution, which is centered around the geometric mean, whereas
clearly unacceptable individual risks come
from the upper end of the distribution.
This risk estimation problem has been
approached by a) extending the exposureresponse relationship for radon progeny exposure and lung cancer observed in the miners to
the general population; and b) attempting to
direcdy estimate risk to the general population
by conducting case-control studies. The former approach is subject to the principal
uncertainties arising from the generalization of
risks observed in male miners, differing
dosimetry of radon progeny in homes and
mines, and extrapolation from higher to lower
exposures. The latter approach, using risk estimates from case-control studies, has proved
more difficult than anticipated when the
studies were initiated. Daunting problems in
estimating exposures to radon indoors
markedly blunt the sensitivity of the casecontrol studies and limit the precision of risk
estimates from their data (9,11,20). These
problems include finding and gaining access
to residences and assuming that contemporaneously measured concentrations reflect past
values. The uncertainties in both approaches
to estimating the risks of lower levels of
indoor radon continue as a source of controversy and ofweakness in the scientific foundation for managing the risk of indoor radon.
The epidemiologic evidence from the
miners will become stronger as more followup time is accrued, particularly from the
more recent cohorts with the lowest exposure.
Additional cohort studies, particularly in
Czechoslovakia (21) and the former East
Germany (22), may also be informative. As
the limitations of the individual case-control
studies were recognized (11), plans were
made to pool the results of the studies for risk
estimation. Although the findings of the individual studies reported to date seemingly have
been inconsistent, when construed (improperly) as positive or negative, meta-analysis
shows the findings to be reasonably consistent
and with evidence of a positive dose-response
relationship, similar to those predicted from
the miner data (1,13). Plans have now been
completed to pool the data from the
case-control studies at the individual participant level. This pooling will bring this line of
investigation to a close, giving the greatest
power and precision presently achievable.
The observational evidence may be
strengthened by improved methods for exposure estimation and by using emerging methods for estimating exposure. The exposure
estimates in the epidemiologic studies of miners are based on limited and incomplete data
and pragmatic approaches [reviewed by the
National Research Council (1)]. Undoubtedly there is substantial random error in the
exposure estimates and possibly systematic
error as well (e.g., systematic over- or underestimation of some exposures). This problem
has long been recognized and biodosimetric
methods have been developed as one potential solution, induding measurement of lead210 (the long-lived radioisotope that ends the
radon progeny decay series) in red blood cells
and in bone, by use of autopsy materials, or
by skull counting. The sensitivity of skull
counting has been enhanced (23), although
not yet to levels sufficient for the lower end of
miner exposure. Nonetheless, skull counting
offers a potential approach for assessing the
degree of error affecting exposure estimates in
the epidemiologic studies and making adjustments using statistical methods considered
below. Using the skull-counting method is
currently being explored in studies of Chinese
tin miners and New Mexico uranium miners.
The problems of exposure estimation in
the case-control studies may be partially surmounted using glass (e.g., covering pictures)
as an exposure indicator. Long-lived progeny
embedded in the surface of glass over time
emit alpha particles, which can be counted as
an index of the concentration of radon to
which the glass has been exposed (24,25).
This approach has now been incorporated
into several of the case-control studies
(26,24-). In a case-control study in Missouri,
Alavanja et al. (27) found a significant, positive relationship between radon exposure and
lung cancer risk, using glass-based exposure
estimates, but not with estimates based on
radon concentration in air. This finding suggests that exposure misclassification was
reduced by using the glass-based estimates.
This technique might be retrospectively used
in other case-control studies to estimate the
degree of exposure misclassification to
accomplish adjustment.
Environmental Health Perspectives * Vol 108, Supplement 4 * August 2000
RADON AND LUNG CANCER RISK: TAKING STOCK
radiation exposure (36). A review of some
recent literature shows that there are numerous surveys documenting indoor concentrations of radon in developing and developed
countries around the world (Table 2).
Although there is likely to be a range of
potential modifying factors among these
countries, particularly cigarette smoking, the
risk models developed by the BEIR VI
Committee and other groups remain relevant
for guiding policy. Extension of these models
to other countries would identify some as
having an unacceptable burden of lung cancer
and the world's total burden of cancers attributable to radon undoubtedly would be large
if estimated. Policy development and implementation is another matter and the relevance
of policies adopted in North America or
Europe is uncertain. Guidance should be
developed by those organizations concerned
with radiation protection internationallythe ICRP and the United Nations.
How Can We Protect and Compensate
Uranium Miners?
The number of men and women who mined
uranium underground in the countries of the
West and of the former Soviet Union will
With new statistical methods for consid- The rate of transformation was substantially
ering measurement error, adjustments can be lower with exactly one hit, leading the
made to risk estimates (28). In the BEIR VI investigators to suggest that risk estimates
report, Thomas and colleagues (29) describe made at higher exposures could overestimate
one approach that is undergoing further elab- risks at low exposures, where only one hit can
oration and Spiegleman and Logan (30) also be expected. This research is illustrative of the
apply measurement error correction methods type of experiment that directly addresses a key
to uranium miner data. These methods will uncertainty in risk estimates for radon (19,32).
We should be moving toward developinflate risk estimates in comparison with
those derived from the uncorrected estimates ment of biologically based risk models, based
on an underlying theory of radon carcinogenused in the analyses to date.
Advances in the understanding of the esis. Findings from the alpha particle irradiamolecular and cellular basis of carcinogenesis tion studies will prove useful in developing
by alpha particles offer the greatest promise such models. Moolgavkar et al. (33) and
for reducing uncertainty in radon risk esti- Luebeck et al. (34) have already applied the
mates. Together, microdosimetric considera- two-stage model of carcinogenesis to data
tions and experimental findings support the from underground miners, illustrating the
theory that a single alpha particle can perma- potential for biologically based modeling of
nently change cellular DNA (1). The assump- epidemiologic data. Parallel analyses of anition of a nonthreshold and linear model at mal data also have been carried out (35).
low doses already appears quite tenable (1). Advances in the underlying biologic basis for
The application of methods for single-cell such models will strengthen this approach.
irradiation will continue to inform risk assessment. For example, Miller et al. (31) exam- Is Radon a Global Public Health
ined the frequency of cell transformation Problem?
following exposure of cell nuclei to exactly Throughout the world, particularly in counone alpha particle, compared with an average tries in temperate and colder climates, indoor
of one particle under a Poisson distribution. radon is probably a dominant contributor to
Table 2. Indoor concentrations of radon: results of surveys.
Country
Italy (47
Russia (48)
Year of survey
1989-1994 - survey began
in March
1995-1996
190
380
253
105
195
653
640
32 Bq m-3
100
99
56.8 Bq m-3
28.5 Bq m-3
Israel (51)
Jordan (52)
1995 - September-December
Jerusalem public school (six
grades, 600 students)
9 major cities (35 zones each)
Hong Kong (53)
Southwest England
1995 - late NovemberMarch 1996
1996 - August-early December
1989-1992
10 underground shopping
centers surveyed; 58 dwelling
sites
1.5 million (28,900 tumors
Poland (55)
1991 - three months
Japan
Hiroshima and
Nagasaki (50)
(54)
Kenya (56)
were counted)
310 detectors randomly
1,099 (lung cancer)
200 water samples
Thailand (57)
1995 - October
387 samples
Idaho (58)
SD, standard deviation.
1994
1,300 groundwater samples
Environmental Health Perspectives
*
Max range
(Bq m-3)
Bq m-3
April-July
October-December
January-March
1993-1994 - in the summer;
morning
1985 - In January two detectors
were placed in 189 houses;
one detector in 11 houses.
Detectors were left until
October 1985
1995- December
Russia (49)
Geometric
SD
2.0
Geometric mean
in pCi/L (Bq m-3)
57 Bq m-3
Dwellings surveyed (no.)
4,866
Vol 108, Supplement 4 * August 2000
115
206
190
180 Bq mi3
2.7
2.2
> 10,000 Bq m3
Radon and thoron concentration levels
Bag dosimeters - 32-107 Bq mi3
Cup dosimeters - 27-88 Bq m-3
29.2 ± 7.8 Bq m3
< 40 Bq m3
> 230
Bq m3
2.2 pCi/L
> 4 pCi/L
222Rn activity concentration ranges
from 0.8 ± 0.5 to 31.7 ± 33.5 Bq L-1
179.74 and
263.38 Bq m-3
17.7 Bq L-'
639
SAMET AND ERADZE
never be known, but an estimate of about
1 million may be reasonable (37). In the
United States, thousands worked in the
Colorado Plateau region (38) and the peak
number of underground workers in the Grants
Uranium belt was as high as 4,000-5,000. We
know now that several hundred thousand miners worked in the former East Germany (39)
and the number who worked in
Czechoslovakia may have been as large. In
China, the epidemiologic cohort of Yunan tin
miners numbers around 17,000 and this is a
selected group from the total population.
Relative risks and attributable risks for lung
cancer in the miner cohorts are high (1), providing strong evidence of an epidemic of occupational lung cancer in the miners. Most
certainly, there will also be high rates of silicosis and silicotuberculosis among miners, and
there is still a question about whether uranium
miners also develop pulmonary fibrosis (1,40).
Uranium exploration and mining began
after World War II in the climate of urgency
spawned by the Cold War and the nuclear
arms competition. The historical record
clearly shows that the health and safety of
underground uranium miners was neglected
in the United States (38,41,42) and almost
certainly in other countries as well.
Unfortunately, many former miners who
developed lung cancer have not received any
compensation in spite of the circumstances
under which they worked. In the United
States, miners or their families sought compensation through the workmens' compensation system with varying success. The
Radiation Exposure Compensation Act,
passed in 1990 (41), offers an apology to the
miners and provides financial compensation
to miners or their families who meet criteria
for exposure and diagnosis. While the act is
well-intentioned, there are evident problems
in its provisions that need to be addressed
through scientifically based revisions (43).
The miner data have been analyzed to
develop a risk model for this purpose, illustrating one potential approach to evidencebased compensation (44). The relationship
between compensation schemes in other
countries and the epidemiologic evidence
should also be evaluated.
Uranium mining continues throughout
the world, although much of the ore production is from surface mines, which fortunately results in relatively low exposures.
Underground mining persists, however
(36,37). The mounting epidemiologic and
experimental evidence indicates that there is
no safe level of radon exposure and a lifetime of working at current exposure limits is
projected to carry an unacceptable risk (1).
Epidemiologic surveillance of currently
exposed underground miners is warranted,
perhaps employing new approaches for
640
monitoring with biomarkers (45,46).
Current and former miners, as a population
at high risk for lung cancer, are also potentially useful sources of information for
studies of chemoprevention and molecular
markers of the early stages of carcinogenesis.
Summary and Conclusions
The story of radon and lung cancer is remarkable for its length and its many twistings and
turnings. We have long known that underground miners are at risk for lung cancer and
have had evidence establishing radon as a
cause of lung cancer since mid-century. A
wealth of epidemiologic data from the underground miners provides a quantitative picture
of the lung cancer risk caused by radon and
these observational data are well buttressed in
a substantial body of experimental evidence.
This body of experimental and observational
evidence has proved informative for estimating the risks of indoor radon, a more recent
problem, and observational studies that
directly estimate the risks of indoor radon
indicate that the indirect approach using the
miner data appears on target. In fact, the
totality of the evidence on radon and lung
cancer is noteworthy for its scope. There are
few carcinogens for which such extensive epidemiologic data are available, particularly
data extending into the range of exposures
experienced by the general population.
Policies for control of radon remain
under attack, however, as does their scientific
basis. Further research drawing on molecular
and cellular approaches and further followup of underground miner cohorts should
help alleviate much remaining criticism.
Within a few decades, we should be able to
construct mechanistically based risk models
that combine epidemiologic and experimental data to yield radon exposure estimates
with enhanced certainty.
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